Synthesis Of N-vinylpyrrolidone Resins For The Adsorption Of Organic Micropollutants From Aquatic Environments

The environmental hazards and potential ecological risks caused by organic micropollutants(OMPs)in the environment are widely concerned.Not only do they endanger the surface water,but also cause great threats to the safety of drinking water.Due to the large variety,difficult degradation,poor biodegradability of OMPs,conventional water treatment technology has been unable to remove them effectively,especially hydrophilic OMPs.Efficient treatment processes for hydrophilic OMPs has caused much attention.The advanced treatment process of adsorption and membrane treatment can improve the removal of OMPs in water,and the most common adsorption treatment is activated carbon adsorption.Activated carbon adsorbent also has lots of shortcomings,such as poor mechanical strength,difficulty of regeneration and reuse,poor adsorption of hydrophilic OMPs,limiting its application.In recent years,synthetic resin adsorbent is widely used in the adsorption of OMPs owing to its designable structure and feasible regeneration.Most of these resins are synthesized with hydrophobic monomer.These resins possess a good adsorption performance on the majority of hydrophobic OMPs in the environmental water body,but its adsorption on hydrophilic OMPs is not satisfactory.In order to improve the adsorption performance of the hydrophilic OMPs,it is urgent to develop a new type of hydrophilic polymer,which is one of the important research fields.Up to date,researches on hydrophilic polymer resins mainly focus on the structure modification of polymers.Introducing the polar groups(acetyl,hydroxymethyl,benzoyl,ortho carboxyl benzene armour acyl,and so on)onto the structure of polymers can enhance the hydrophilicity of the polymer resins.However,few studies have investigated the polymer resins synthesized with hydrophilic monomer.N-vinyl pyrrolidone(NVP),a kind of water-soluble compounds with non-toxicity,hydrophilicity,and high complexation ability,can polymerize with unsaturated vinyl monomers and form special characteristics polymers.At present,NVP polymer has been rarely reported and the only product is the packing of Oasis HLB extraction cartridge(HLB)produced by Waters Company.Due to the characteristics of the hydrophilic and lipophilic properties of this material,it is widely used in the pre-treatment of OMPs samples because of its good adsorption and desorption properties.And the synthesis technology of HLB has been in a state of secrecy,there is no report related to the preparation method in China.Oasis HLB extraction cartridges are mainly imported at a high price.Based on the background above,NVP is employed as a co-monomer to synthesize N-vinylpyrrolidone resin in this study.The research of physical-chemical properties of N-vinylpyrrolidone resin and its adsorption performance on OMPs were carried out.The main contents and conclusions were as follows:(1)The ingredient for preparation of N-vinylpyrrolidone resin was determined through optimizing the dosages of monomer,initiating agent,porogen,and the composition of aqueous phase.N-vinylpyrrolidone resin(NVPD-1)with high specific surface area was synthesized.Results showed that the dosage of NVP had a great influence on the pore structure of resin polymers.When the dosage of NVP was 75%,the resin had the largest specific surface area(613.23 m2/g).When the dosages of toluene was 50%,the resin had more abundant pore structure.Compared with gelatin,the size of the resins prepared with polyvinyl alcohol as dispersant were smaller,and the average particle size of resin was about 60 ?m.(2)The order of adsorption capacity of tetracycline(TC)by resins with different NVP content was:NVPD-a<NVPD-c<NVPD-e<NVPD-f<NVPD-g>NVPD-h.NVPD-g had a maximum adsorption capacity(258.76 mg/g)for TC,which was directly related to its maximum surface area.Adsorption kinetic showed that the adsorption process of NVPD-a was more suitable for the pseudo-first-order kinetic,while NVPD-c,NVPD-e and NVPD-g were more suitable for the pseudo-second-order kinetic.The adsorption kinetic of NVPD-a was different with others because NVPD-a was polydivinylbenzene copolymers and only physical adsorption existed in the adsorption process.The adsorption of TC by NVPD-c,NVPD-e and NVPD-g were affected by the diffusion of particles.In the presence of humic acid,the removal efficiency of NVPD-g was enhanced.Humic acid may have the adsorption bridging function,resulting in the increase of the adsorption capacity of TC.The saturated NVPD-g can be regenerated by methanol,with the rate of desorption about 98%.Results indicated that NVPD-g had good adsorption and regeneration performance.(3)Phenol,4-nitrophenol,and bisphenol A were chosen as target pollutants.By investigating the adsorption performance of NVPD-1 and XAD-4 on the phenolic compounds,it was found that the adsorption capacity of NVPD-1 was higher than that of XAD-4.Adsorption thermodynamics of phenolic compounds of the two types of resin was more suitable to the Freundlich model,indicating that the adsorption process of phenolic compounds was a heterogeneous multilayer adsorption.This result also showed that pore-filling and capillary condensation existed in the adsorption process.The adsorption capacity at acidic condition was larger than that of alkaline conditions.The adsorption of NVPD-1 on phenolic compounds depended on the contribution of hydrophobic effect,electrostatic interactions,H-bonding,?-? EDA interactions and cation-? bonding,and the contribution varied under different pH.The adsorption of phenolic compounds on NVPD-1 and XAD-4 were not affected by NaCl,which showed that ion exchange did not dominate in the adsorption process.Due to the salting out effect,CaCl2 can promote the adsorption of phenol and 4-nitrophenol.Humic acid could promote the adsorption of phenol by NVPD-1 and XAD-4.In the desorption experiment,methanol had a high desorption efficiency(99%)for NVPD-1.After five adsorption-desorption cycles,the adsorption performance of NVPD-1 resin maintained high.(4)Sulfadiazine,sulfadimethoxine,sulfadimidine,and sulfamethoxazole were chosen as target pollutants.By investigating the adsorption performance of NVPD-1,HLB,and XAD-4,it was found that the adsorption capacity of sulfadiazine,sulfadimethoxine,sulfadimidine,and sulfamethoxazole on NVPD-1 were higher than that of HLB and XAD-4.The adsorption capacity of NVPD-1 on sulfadiazine,sulfadimidine,sulfamethoxazole increased dramatically with the increase of substrate concentration,which was related to the abundant microporous of NVPD-1.The adsorption equilibrium of HLB on sulfonamides could reach in 100 minutes,but NVPD-1 and XAD-4 resin needed more time.The adsorption capacity at acidic condition was much larger than that of alkaline conditions.NaOH and methanol had good desorption efficiencies on NVPD-1,and the mixture of them could enhance the desorption performance.After ten consecutive adsorption-desorption cycles,NVPD-1 still maintained high adsorption performance.The excellent adsorption and regeneration performance indicate that NVPD-1 has a promising application in water treatment.